The present invention relates to shield apparatus, especially for use in driving tunnels or similar excavations underground or for use in mine workings.
Drive shields are known which employ one or more frames supporting a plurality of displaceable drive members which contact the wall of a tunnel. The drive members are advanced individually or in groups by means of hydraulic rams. It is also known to construct the frames of shield apparatus so that they can be expanded to brace against the wall of the tunnel. In German patent specification No. 2314703 for example, a shield is described which has drive members or cutters supported and guided on frames which are composed of two components pivotably interconnected at the roof and carried by hydraulic props. The frame components are also connected together at the floor by means of a beam which can be varied in length by means of piston and cylinder units. Another type of shield apparatus is described in German Patent specification No. 2021734. In this shield apparatus, the frames carrying the drive members are extendible or retractible so that in the retracted or contracted position the frames can be easily advanced while in the extended or expanded position they brace the shield and urge the drive members primarily against the roof of the tunnel wall. To provide for the expansion and contraction of the frames, these frames are composed of components connected together through expansion devices in the form of hydraulic piston and cylinder units.
In the known shield apparatuses which utilize expandible frames it is sometimes difficult to ensure stability and during operation pivot joints and the expansion devices can sometimes by subjected to unduly high transverse bending forces which can cause damage.
A general object of the present invention is to provide an improved shield apparatus.